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The purpose of this change is to allow the overriding of one egg, which in turn affects all dependents of that eggs.
79 lines
2.6 KiB
Markdown
79 lines
2.6 KiB
Markdown
# CHICKEN {#sec-chicken}
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[CHICKEN](https://call-cc.org/) is a
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[R⁵RS](https://schemers.org/Documents/Standards/R5RS/HTML/)-compliant Scheme
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compiler. It includes an interactive mode and a custom package format, "eggs".
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## Using Eggs {#sec-chicken-using}
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Eggs described in nixpkgs are available inside the
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`chickenPackages.chickenEggs` attrset. Including an egg as a build input is
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done in the typical Nix fashion. For example, to include support for [SRFI
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189](https://srfi.schemers.org/srfi-189/srfi-189.html) in a derivation, one
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might write:
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```nix
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buildInputs = [
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chicken
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chickenPackages.chickenEggs.srfi-189
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];
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```
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Both `chicken` and its eggs have a setup hook which configures the environment
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variables `CHICKEN_INCLUDE_PATH` and `CHICKEN_REPOSITORY_PATH`.
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## Updating Eggs {#sec-chicken-updating-eggs}
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nixpkgs only knows about a subset of all published eggs. It uses
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[egg2nix](https://github.com/the-kenny/egg2nix) to generate a
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package set from a list of eggs to include.
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The package set is regenerated by running the following shell commands:
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```
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$ nix-shell -p chickenPackages.egg2nix
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$ cd pkgs/development/compilers/chicken/5/
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$ egg2nix eggs.scm > eggs.nix
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```
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## Adding Eggs {#sec-chicken-adding-eggs}
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When we run `egg2nix`, we obtain one collection of eggs with
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mutually-compatible versions. This means that when we add new eggs, we may
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need to update existing eggs. To keep those separate, follow the procedure for
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updating eggs before including more eggs.
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To include more eggs, edit `pkgs/development/compilers/chicken/5/eggs.scm`.
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The first section of this file lists eggs which are required by `egg2nix`
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itself; all other eggs go into the second section. After editing, follow the
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procedure for updating eggs.
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## Override Scope {#sec-chicken-override-scope}
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The chicken package and its eggs, respectively, reside in a scope. This means,
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the scope can be overridden to effect other packages in it.
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This example shows how to use a local copy of `srfi-180` and have it affect
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all the other eggs:
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```nix
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let
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myChickenPackages = pkgs.chickenPackages.overrideScope' (self: super: {
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# The chicken package itself can be overridden to effect the whole ecosystem.
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# chicken = super.chicken.overrideAttrs {
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# src = ...
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# };
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chickenEggs = super.chickenEggs.overrideScope' (eggself: eggsuper: {
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srfi-180 = eggsuper.srfi-180.overrideAttrs {
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# path to a local copy of srfi-180
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src = ...
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};
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});
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});
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in
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# Here, `myChickenPackages.chickenEggs.json-rpc`, which depends on `srfi-180` will use
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# the local copy of `srfi-180`.
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# ...
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```
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